1. Field of the Invention
This invention relates to particularly superior hard films and more particularly, it is concerned with anti-wear material coated articles which comprise, as substrate, a cutting tool or the like made of tungsten carbide or cermet or ceramic.
2. Description of the Prior Art
Coating the surfaces of high speed tool-steel tools, cemented carbide tools and the like with titanium-based nitride or carbide having hardness in order to improve properties such as wear resistance is a well-known technique.
Films of TiN or TiC, deposited by means of ion-plating method, are generally used as the wear resistant coatings for the cutting tools or the like. In particular the TiN film has been widely used in practice because it exhibits high oxidation resistance compared to the TiC film. Namely the TiN films are superior in heat resistance to the TiC films and thus the TiN coated on the surface of the inserts prevents the film from further oxidation, such oxidation being manifested by crater depth at the high temperatures induced by the cutting operations. On the other hand, the film hardness of TiC is greater than that of TiC films are superior, in terms of the width of flank wear, to the TiN films. Recently there has been a need to further increase the cutting speed of tools under increasingly severe conditions. The conventional films, such as the TiN films described above have difficulty in meeting these needs. Further, as the films have excellent heat resistance and hardness properties, films of (Ti, Al)N, (Ti, Hf)N and the like, formed by ion-plating or sputtering have been proposed.
The (Ti, Al)N and (Ti, Hf)N films, however, have the following disadvantages; (i) in the above films, the internal stress is substantially twice as high as that in the TiN films: (ii) with a further increase in film thickness with the aim of improving wear resistance, the internal stress monotonically increases, thus often causing the generation of cracks and the peeling of the films. Accordingly the thickness of the (Ti, Al)N or (Ti, Hf)N films used has to be thinner than in the case of the TiN films, which prevents the full exploitation of their other excellent properties.